SACCOMYIDAI—SUBFAMILY PEROGNATHIDIN A. 495 
a third subfamily. In such case, some tew of the characters of the three 
would be as follows : — 
Diropomyin&.—Molars rootless; upper incisors compressed, sulcate 
Temporal region enormously inflated. Pelage comparatively soft. 
PeroGNatTHipIna&.—Molars rooted; upper incisors compressed, suleate. 
Temporal region moderately inflated. Pelage comparatively hispid. 
Heteromyiw2.—Molars rooted; upper incisors broad, smooth. Tem- 
poral region “ not inflated”. Pelage ‘‘mixed with flattened spines”. 
SuBrAMILY PHEROGNATHIDIN A. 
= Perognathus (genus), of AUTHORS. 
= Perognathidinw, Cougs, Proc. Phila. Acad. 1875, 278. 
The characters of the group having been already sufticiently elucidated, 
it remains to note the two genera by which it is represented in North Amer- 
357-359) a more satisfactory account of the characters of the genus thau I have seen elsewhere, As this 
account furnishes important information pertinent to the general subject, I transcribe his diagnosis of 
the genus, and give a version of those portions of the description of the species which tend to further 
elucidate the generic characters. 
“Dentes incisivi pagina antica laevigati exserti, molares = complicati radicati; labrum integrum; 
rictus perparvus ; rostrum prominens, rhinario nudo; sacculi buccules externi pilosi ; auriculae mediocres ; 
vellus setosum, setis lanceolatis, canaliculatis; pedes pentadactyli; cauda annulata, brevipilosa. Os 
interparietale latum, tempora non inflata. . 
“ Habitus of Mus. Thamb prominent, with rounded nail, shorter than the other digits, which run 
5th, 2d, 4th, and 3d, the latter longest. Relative lengths of the digits of the hind foot as in Isomys ; 5th 
but little longer than 1st, 3d longest ; claws rather longer than those of the fore foot, that of the 2d toe 
longest, convex on the inner side, flat ou the outer. Soles naked, with the usual tubercles. Incisors 
compressed, the horizontal cross-section triangular, with rounded hinder angle, and apparently broader 
than long. Molar series parallel ; last molar in each jaw smallest ; 2d and 3d upper molars of equal size 
and notably smaller than the 1st; anterior molar of lower jaw but little larger than the next two.... 
- “Tneisors yellow, the lower paler colored than the upper. Anterior superior molar with three 
separate enamel-tabes—an anterior, longer and narrower,a posterior shorter and broader, and a third 
much smaller oval one on the inner side of the tooth in a recess where the other two stand apart; 
second upper molar with a deep internal and slight external emargination, or fold of enamel ; third with 
a slight exterior emargination, which is either continuous with a transversely-elliptical interior island 
of enamel, thus forming a deep enamel-fold, or else only just reaches this island without fusing with it ; 
back upper molar with the enamel-pattern like that of the second one, but the posterior half of the 
tooth considerably smaller than the anterior portion. 
“Anterior inferior molar with two enamel-tubes, the anterior of which, somewhat smaller than 
the other, is emarginate before and behind ; the three following teeth with a deep inner and slight outer 
emargination, as on the upper teeth, which are either separated or fused together, in which latter case 
two separate enamel-tubes result. 
“The rostral portion of the skull is narrow ; the nasal bones and intermaxillaries project beyond 
the incisors as in allied genera, and the intermaxillaries form anteriorly a sharp perpendicular ridge. 
The structure of the small incisive foramina, the shave of the lachrymal bones and infraorbital foramina 
are quite as in Geomys. The latter are wholly in the superior maxillary and are separate from the 
nasal cavity. Since, however, the bony septum is in this case extremely thin, and easily mutilated, the 
deceptive appearance of communication between tbe infraorbital foramina and the nasal passages may 
be accidentally produced. The frontal bone, as in Mus, forms a sharp supraorbital ridge, which continues 
on to the parietal, thus forming with its fellow of the opposite side the boundary of a level area, with 
which the interparietal, twice as broad as long, is posteriorly continuous, whilst the temporal fossa is 
excavated [a strong character of Heleromyine—there is no such formation in Perognath.dinw.—Tnr.]. The 
lower jaw strongly resembles that of Perognathus in the form of the coronoid process and mandibular 
angle; the deep pit which is found in Geomus to the outer side of the posterior molar is here wanting.” 
